Southey enlisted as a
private in the 19th (Service) Battalion (
2nd Public Schools),
Royal Fusiliers (City of London) Regiment, with
regimental number 6741. On 26 June 1915 the 19th Battalion became part of the
98th Brigade in the
33rd Division, and Southey was with them when they were sent to France in November 1915. and after completing his flight training was appointed a flying officer and confirmed in his rank on 12 February 1917. Southey flew the
Bristol F.2 two-seater fighter with
No. 48 Squadron through early 1917, making no victory claims, and was wounded when shot down on 4 June. He was promoted to lieutenant on 5 February 1918, before returning to action in March when he joined
No. 84 Squadron to fly the
S.E.5a single-seat fighter. He was credited with twenty aerial victories between May and October 1918, and was appointed a
flight commander with the acting-rank of captain on 14 July 1918. Southey was awarded his first
Distinguished Flying Cross on 2 November 1918. His citation read: :Lieutenant (Temporary Captain) Walter Alfred Southey. ::"A gallant and skilful officer. On the 9th August, observing a large body of enemy troops and artillery on a road, he descended to 50 feet and bombed them, causing heavy casualties; he then engaged them with machine-gun fire, inflicting further loss and scattering them in all directions. He displays great courage in the air, having accounted for seven enemy aircraft." Southey's
Bar to his Distinguished Flying Cross was
gazetted on 7 February 1919. His citation read: :Lieutenant (Acting Captain) Walter Alfred Southey, DFC. ::"An officer of ready resource whose skilful leadership is of the greatest value to his squadron. Since 23rd August Captain Southey has destroyed five enemy kite balloons and three machines, while he has also driven down two aircraft completely out of control." After the end of the war Southey was discharged from RAF service, being transferred to the RAF's unemployed list on 9 March 1919. His tally of 20 victories was made up of five
observation balloons destroyed, eight aircraft destroyed (two shared), and seven driven down out of control (one shared).
List of aerial victories ==Death==